Diabetes refers to a disease process derived from multiple causative factors and characterized by elevated levels of plasma glucose or hyperglycemia along with sugar, fat and protein metabolism disorder caused by insulin secretion and/or the action defects. Diabetes is an ancient disease, and due to the human body absolute or relative lack of insulin resulting in increased concentrations of glucose in the blood which largely discharges in urine with more drink, more urine, more food, weight loss, dizziness, weakness and other symptoms.
Dipeptidyl peptidase-IV (DPPIV) is a serine protease which cleaves N-terminal dipeptides from a peptide chain containing, preferably, a proline residue in the penultimate position. Although the biological role of DPPIV in mammalian systems has not been completely established, it is believed to play an important role in neuropeptide metabolism, T-cell activation, attachment of cancer cells to the endothelium and the entry of HIV into lymphoid cells (WO98/19998).
More recently, it was discovered that DPPIV is responsible for inhibiting the secretion of glucagon-like peptide (GLP)-1. More particularly, DPPIV cleaves the amino-terminal His-Ala dipeptide of GLP-1, degrading active GLP-1(7-36)NH2 into inactive GLP-1(9-36)NH2 (Endocrinology, 1999, 140: 5356-5363). Under the physiological condition, the half-life of the whole GLP-1 in blood circulation is short, the inactive metabolite from GLP-1 degraded by DPPIV can combine with GLP-1 receptor to antagonize the active GLP-1, so the physiological response to GLP-1 is shortened. The endogenous even exogenous GLP-1 can be entirely protected by the DPPIV inhibitor from being deactivated by DPPIV, and the GLP-1 bioactivity can be significantly increased (5- to 10-fold). Since GLP-1 is a major stimulator of pancreatic insulin secretion and can directly effect on glucose disposal, the DPPIV inhibitor is well useful for treating non-insulin-dependent diabetes mellitus (NIDDM) (U.S. Pat. No. 6,110,949).